1. Field of the Invention
This invention relates to a small electronic apparatus equipped with a generator which converts mechanical energy obtained by the rotational or reciprocating motion of a rotary weight to electrical energy, especially to a small electronic apparatus equipped with a generator, which exhibits improved impact resistance in a mechanical power transmission mechanism in the generator and exhibits improved generating efficiency.
2. Description of the Background Art
An electronic wristwatch is one of small electronic apparatuses in which mechanical energy obtained by rotary motion or reciprocating motion of a rotary weight is converted into electric energy, enabling the apparatuses to be operated.
In a generator of such an electronic wristwatch, there is a problem that when the rotary weight is hit by a strong impact caused by dropping the wristwatch or the like, support materials, gears, and pinion gears for the mechanical power transmission mechanism of the rotary weight are damaged or the ICs are broken.
There have been methods disclosed, for example, in Japanese Patent Application Laid-open No. 128286/1988 aiming to avoid damages to the mechanical power transmission mechanism of the rotary weight to improve the impact resistance.
Specifically, a device disclosed in Japanese Patent Application Laid-open No. 128286/1988 comprises a slip device which transfers motive force to the power transmission mechanism by a frictional force. The slip device slips to avoid transfer of a strong impact load torque applied to the power transmission mechanism when a strong impact is applied to the rotary weight. Also, the rotational velocity transferred to the rotor is restrained by the slip action of the slip device to protect the charge control circuit from damages caused by a high voltage induced in a coil for a generator because of high rotation of a generator rotor due to an impact on the rotary weight.
Almost the same method as in Japanese Patent Application Laid-open No. 128286/1988 is disclosed in International Patent Application Laid-open No. W089/06833.
Also, as prior art, FIG. 5 described in Japanese Patent Application Laid-open No. 91992/1991 shows the provision of a rotary weight itself provided with a spring structure which is resistant to an impact on the rotary weight. By this prior art, the effect of absorbing an impact torque in the direction along the rotation of the rotary weight can be expected.
However, in the prior art of Japanese Patent Application Laid-open No. 128286/1988 and International Patent Application laid-open No. W089/06833, in which the slip device is provided in the power transmission mechanism of the rotary weight, it is necessary to reduce the slip torque to less than the mechanical strength limit of tenons, gears, or the like. The slip torque must be designed to have a considerably small value taking safety into consideration.
If the rotational force transferred to the power transmission mechanism of the rotary weight is higher than the slip torque, the slip device assembled in the power transmission mechanism slips to run idle with the rotation of the rotary weight. Therefore, the rotor does not follow the rotation, resulting in a reduction in generating efficiency.
In the prior art shown in FIG. 5 in Japanese Patent Application Laid-open No. 91992/1991, in which the rotary weight itself is provided with the spring structure, if it is intended to provide the rotary weight with an appropriate spring structure to prevent the power transmission mechanism from destructive impact, the stiffness of the rotary weight itself is reduced. When the rotary weight is subjected to a strong impact, it tends to be deformed.
This invention has been achieved in view of this situation and has an object of providing a small electronic apparatus equipped with a generator having a high generating efficiency without slip, differing from the conventional power transmission mechanism.
Another object of the present invention is to provide a small electronic apparatus provided with a generator which protects the power transmission mechanism from destructive impact, differring from the conventional power transmission mechanism, even if such destructive impact is applied to a rotary weight.